1. Field of the Invention
The present invention relates to a method for preparing a sulfonated organic porous material comprising an organic porous material with a specific structure with homogeneously introduced sulfonic acid groups.
2. Description of Background Art
As a porous material having a continuous pore structure comprising mesopores existing on the walls of interconnected macropores, an inorganic porous material formed from silica and the like are known (Patent Document 1: U.S. Pat. No. 5,624,875). Development of application of the inorganic porous material as a filler for chromatography has actively been undertaken. However, since this inorganic porous material is hydrophilic, complicated and expensive procedures such as a hydrophobicizing treatment of the surface and the like are required to use it as an adsorbent. In addition, when retained in water for a long period of time, the inorganic porous material releases in water silicate ion produced by hydrolysis of silica. Therefore, it is impossible to use the inorganic porous material as an ion-exchanging material for producing purified water and high purity water. On the other hand, if used as a filler for chromatography, the inorganic porous material has been reported to exhibit remarkably improved performance over conventional particulate fillers. However, since mesopores cannot be greater than 50 μm in size due to the manufacturing method restraints, there has been a restriction imposed on a process in which a material is processed at a large flow rate under a low pressure.
As organic porous materials having continuous pores, porous materials possessing a particle aggregation-type structure have been disclosed in F. Svec, Science, 273, 205–211(1996) (Non-patent Document 1) and other publications. The porous material obtained by this method has a small pore volume and an insufficient mesopore size due to the particle aggregation-type structure. For these reasons, a limitation is imposed on application of the pore material in a process with a large flow rate under a low pressure. In addition, since conventional organic porous materials and porous ion-exchanging materials, made by introducing ion exchange groups into conventional organic porous materials, have many internal structural defects and possess low strength and poor durability against swelling and shrinkage, these organic porous materials exhibit only insufficient separating performance when used as a filler for chromatography. Therefore, development of an organic porous material having a large pore volume and high physical strength, containing pores with a large and uniform pore diameter, being free from internal structural defects such as macrovoids, and having a continuous pore structure has been strongly desired.
Furthermore, manufacture processes of conventional organic porous materials had drawbacks such as significant unevenness in the quality of manufactured products in each production lot and difficulty in reproducing the manufacturing process. Therefore, development of an organic porous material having a large pore volume and high physical strength, containing pores with a large and uniform pore diameter, being free from internal structural defects such as macrovoids, and having a continuous pore structure, as well as development of a manufacturing process that can produce such an organic porous material, has been strongly desired.
On the other hand, as the method for sulfonating organic high molecular weight compounds, a method of sulfonating using fuming sulfuric acid, chlorosulfuric acid, or concentrated sulfuric acid in a liquid phase has been commonly used. Japanese Patent Application Laid-open No. 4-49562 (Patent Document 2) discloses a method of introducing ion exchange groups. This method converts chloromethyl groups and quaternary ammonium groups introduced into an organic porous material having a continuous porous structure into sulfonic acid groups by a functional group conversion reaction. A drawback of this method is that a long time is required for the sulfonation reaction, since the sulfonation agent takes a considerably long period time to infiltrate the porous structure.
Japanese Patent Application Laid-open No. 3-269160 (Patent Document 3) discloses a method of continuously sulfonating polyolefin nonwoven fabrics by a treatment with sulfuric anhydride gas. A sheet-like material can be sulfonated in a comparatively short period of time using this method. However, sulfonated materials are limited to a sheet, fabrics, nonwoven fabrics, and the like. There are no descriptions relating to sulfonation of an organic porous material having a continuous pore structure comprising mesopores existing on the walls of interconnected macropores. Since only the surface of polyolefin nonwoven fabric is sulfonated using the above sulfonation method, only a vary small amount of sulfonic acid groups can be introduced.    Patent Document 1: U.S. Pat. No. 5,624,875 (Summary, claim 1, and Example 7)    Nonpatent Document 1: F. Svec, Science, 1996, vol. 273, 205–211    Patent Document 2: Japanese Patent Publication No. 4-49562 (Example 5)    Patent Document 3: Japanese Patent Application Laid-open No. 3-269160 (claim 1, page 5, left lower column)
A subject to be solved in the present invention is to provide a method for preparing a sulfonated organic porous material capable of homogeneously introducing a large amount of sulfonic acid groups into an organic porous material with a specific structure in a short period of time.